Etching method

ABSTRACT

An etching method performed by an etching apparatus includes a first process of causing a first high-frequency power supply to output a first high-frequency power with a first frequency and causing a second high-frequency power supply to output a second high-frequency power with a second frequency lower than the first frequency in a cryogenic environment where the temperature of a wafer is −35° C. or lower, to generate plasma from a hydrogen-containing gas and a fluorine-containing gas and to etch, with the plasma, a multi-layer film of silicon dioxide and silicon nitride and a single-layer film of silicon dioxide that are formed on the wafer; and a second process of stopping the output of the second high-frequency power supply. The first process and the second process are repeated multiple times, and the first process is shorter in time than the second process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/375,405 filed on Dec. 12, 2016, which is basedupon and claims the benefit of priority of Japanese Patent ApplicationNo. 2015-247568 filed on Dec. 18, 2015 and Japanese Patent ApplicationNo. 2016-110071 filed on Jun. 1, 2016, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

An aspect of this disclosure relates to an etching method.

2. Description of the Related Art

There exists a method where holes with a high aspect ratio are etched ina silicon dioxide film under a low-temperature environment (see, forexample, Japanese Laid-Open Patent Publication No. 07-22393). Forexample, in producing a three-dimensional multilayer semiconductormemory, this method makes it possible to etch holes or grooves with ahigh aspect ratio in a multi-layer film of silicon dioxide and siliconnitride and in a single-layer film of silicon dioxide.

-   [Patent document 1] Japanese Laid-Open Patent Publication No.    07-22393-   [Patent document 2] Japanese Laid-Open Patent Publication No.    62-50978-   [Patent document 3] Japanese Laid-Open Patent Publication No.    07-22149-   [Patent document 4] Japanese Patent No. 2956524

With the above method, however, when the multi-layer film and thesingle-layer film are processed concurrently, the processing timebecomes long and the productivity is reduced due to the difference inthe etching rate between the multi-layer film and the single-layer film.

Also, in plasma etching, it is important to prevent the increase in thetemperature of a substrate due to heat input from plasma and to evenlyetch a multi-layer film of silicon dioxide and silicon nitride and asingle-layer film of silicon dioxide.

SUMMARY OF THE INVENTION

In an aspect of this disclosure, there is provided an etching methodperformed by an etching apparatus including a first high-frequency powersupply and a second high-frequency power supply. The etching methodincludes a first process of causing the first high-frequency powersupply to output a first high-frequency power with a first frequency andcausing the second high-frequency power supply to output a secondhigh-frequency power with a second frequency lower than the firstfrequency in a cryogenic environment where the temperature of a wafer is−35° C. or lower, to generate plasma from a hydrogen-containing gas anda fluorine-containing gas and to etch, with the plasma, a multi-layerfilm of silicon dioxide and silicon nitride and a single-layer film ofsilicon dioxide that are formed on the wafer; and a second process ofstopping the output of the second high-frequency power supply. The firstprocess and the second process are repeated multiple times, and thefirst process is shorter in time than the second process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing illustrating an exemplary configuration of anetching apparatus;

FIG. 2 is a drawing illustrating exemplary methods of etching amulti-layer film and a single-layer film under a cryogenic environment;

FIG. 3 is a flowchart illustrating an exemplary intermittent etchingprocess according to a first embodiment;

FIGS. 4A and 4B are drawings illustrating changes in a wafer temperaturein an intermittent etching process and a continuous etching process;

FIGS. 5A through 5C are drawings illustrating the shapes of holes formedby an intermittent etching process and a continuous etching process;

FIG. 6 is a flowchart illustrating an exemplary intermittent etchingprocess according to a second embodiment;

FIGS. 7A through 7C are drawings illustrating the shapes of holes formedby intermittent etching processes with different duty ratios;

FIGS. 8A and 8B are drawings illustrating etching methods according to athird embodiment; and

FIGS. 9A and 9B are drawings illustrating the results of etchingprocesses according to the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below with referenceto the accompanying drawings. Throughout the specification and thedrawings, the same reference number is assigned to substantially thesame components, and repeated descriptions of those components areomitted.

<<Overall Configuration of Etching Apparatus>>

An exemplary configuration of an etching apparatus 1 according to anembodiment is described with reference to FIG. 1. FIG. 1 is a drawingillustrating an exemplary configuration of the etching apparatus 1.

The etching apparatus 1 includes a cylindrical process chamber 10comprised of, for example, aluminum whose surface is alumite-treated (oranodized). The process chamber 10 is grounded.

A mount table 17 is provided in the process chamber 10. The mount table17 is comprised of, for example, aluminum (Al), titanium (Ti), orsilicon carbide (SiC), and is supported via a holding part 14 havinginsulating properties by a support 16. With this configuration, themount table 17 is disposed on the bottom of the process chamber 10.

An evacuation pipe 26 is provided at the bottom of the process chamber10, and the evacuation pipe 26 is connected to an evacuation device 28.The evacuation device 28 is implemented by a vacuum pump such as a turbomolecular pump or a dry pump. The evacuation device 28 reduces thepressure of a process space in the process chamber 10 to a predeterminedvacuum pressure, and discharges a gas in the process chamber 10 via anevacuation channel 20 and an evacuation port 24. A baffle plate 22 isplaced in the evacuation channel 20 to control the flow of the gas.

A gate valve 30 is provided on the side wall of the process chamber 10.A wafer W is carried into and out of the process chamber 10 by openingthe gate valve 30.

A first high-frequency power supply 31 for generating plasma isconnected via a matching box 33 to the mount table 17. Also, a secondhigh-frequency power supply 32 for attracting ions in the plasma to thewafer W is connected via a matching box 34 to the mount table 17. Thefirst high-frequency power supply 31 applies, to the mount table 17,first high-frequency power HF (high-frequency power for plasmageneration) with a first frequency of, for example, 60 MHz, which issuitable to generate plasma in the process chamber 10. The secondhigh-frequency power supply 32 applies, to the mount table 17, secondhigh-frequency power LF (high-frequency power for bias voltagegeneration) with a second frequency of, for example, 13.56 MHz, which islower than the first frequency and is suitable to attract ions in theplasma to the wafer W on the mount table 17. For example, the secondhigh-frequency power LF is applied in synchronization with the firsthigh-frequency power HF. Thus, the mount table 17 functions as a tableon which the wafer W is placed as well as a lower electrode.

An electrostatic chuck 40 for holding the wafer W with electrostaticattraction is provided on an upper surface of the mount table 17. Theelectrostatic chuck 40 includes an electrode 40 a made of a conductivefilm and a pair of insulating layers 40 b (or insulating sheets)sandwiching the electrode 40 a. A direct voltage source 42 is connectedvia a switch 43 to the electrode 40 a. When a voltage from the directvoltage source 42 is applied, the electrostatic chuck 40 attracts andholds the wafer W with Coulomb force. A temperature sensor 77 isprovided on the electrostatic chuck 40 to measure the temperature of theelectrostatic chuck 40. The temperature sensor 77 can measure thetemperature of the wafer 40 on the electrostatic chuck 40.

A focus ring 18 is disposed on the periphery of the electrostatic chuck40 to surround the mount table 17. The focus ring 18 may be comprisedof, for example, silicon or quartz. The focus ring 18 functions toimprove the in-plane uniformity of etching.

A gas shower head 38 is provided on the ceiling of the process chamber10. The gas shower head 38 functions as an upper electrode that is at aground potential. With this configuration, the first high-frequencypower HF from the first high-frequency power supply 31 is applied to a“capacitor” formed between the mount table 17 and the gas shower head38.

The gas shower head 38 includes an electrode plate 56 having multiplegas holes 56 a, and an electrode support 58 that detachably supports theelectrode plate 56. A gas supply source 62 supplies a process gas via agas supply pipe 64 and a gas inlet 60 a into the gas shower head 38. Theprocess gas diffuses in a gas diffusion chamber 57, and is introducedvia the gas holes 56 a into the process chamber 10. Ring-shaped orconcentric magnets 66 are disposed around the process chamber 10 tocontrol plasma generated in a plasma generation space between the upperelectrode and the lower electrode with a magnetic force.

A heater 75 is embedded in the electrostatic chuck 40. Instead of beingembedded in the electrostatic chuck 40, the heater 75 may be attached tothe back surface of the electrostatic chuck 40. An electric currentoutput from an alternating-current power supply 44 is supplied via afeeder line to the heater 75. With this configuration, the heater 75heats the mount table 17.

A refrigerant pipe 70 is formed in the mount table 17. A refrigerant (orbrine) supplied from a chiller unit 71 circulates through therefrigerant pipe 70 and a refrigerant circulation pipe 73 to cool themount table 17.

With the above configuration, the mount table 17 is heated by the heater75, and is cooled by the brine having a predetermined temperature andflowing through the refrigerant pipe 70 in the mount table 17. Thisconfiguration makes it possible to adjust the temperature of the wafer Wto a desired value. Also, a heat transfer gas such as a helium (He) gasis supplied via a heat-transfer gas supply line 72 to a space betweenthe upper surface of the electrostatic chuck 40 and the lower surface ofthe wafer W.

The controller 50 includes a central processing unit (CPU) 51, aread-only memory (ROM) 52, a random access memory (RAM) 53, and a harddisk drive (HDD) 54. The CPU 51 performs etching such as plasma etchingaccording to procedures defined by recipes stored in a storage such asthe ROM 52, the RAM 53, or the HDD 54. The storage also stores varioustypes of data such as a data table described later. The controller 50controls the temperatures of a heating mechanism including the heater 75and a cooling mechanism using the brine.

When plasma etching is performed, the gate valve 30 is opened, and thewafer W is carried into the process chamber 10 and placed on theelectrostatic chuck 40. After the wafer W is carried into the processchamber 10, the gate valve 30 is closed. The pressure in the processchamber 10 is reduced to a preset value by the evacuation device 28.Also, a voltage is applied from the direct voltage source 42 to theelectrode 40 a of the electrostatic chuck 40 toelectrostatically-attract the wafer W to the electrostatic chuck 40.

Next, a gas is introduced via the gas shower head 38 into the processchamber 10 like a shower, and the first high-frequency power HF of apredetermine level for plasma generation is applied to the mount table17. The introduced gas is ionized and dissociated by the firsthigh-frequency power HF to generate plasma, and plasma etching isperformed on the wafer W by the plasma. The second high-frequency powerLF for generating a bias voltage may also be applied to the mount table17. After the plasma etching, the wafer W is carried out of the processchamber 10.

<<Etching Method>>

Next, an exemplary etching method for etching the wafer W with plasmagenerated by the etching apparatus 1 is described. When a multi-layerfilm 12 of silicon dioxide and silicon nitride and a single-layer film13 of silicon dioxide are processed concurrently as illustrated by FIG.2 (b) and the etching rates (ER) of these films are different from eachother, the processing time becomes long and the productivity is reduced.

For the above reason, in an etching method according to an embodiment,in a cryogenic environment where the temperature of the lower electrode(the mount table 17) is less than or equal to −60° C., the etching ratesof the multi-layer film 12 and the single-layer film 13 formed on thewafer W are substantially equalized.

The single-layer film 13 of silicon dioxide and the multi-layer film 12of alternately-stacked silicon dioxide and silicon nitride films areformed on the wafer W, and a mask film 11 is formed on the multi-layerfilm 12 and the single-layer film 13. The wafer W is, for example, asilicon wafer. The mask film 11 is, for example, a polysilicon film, anorganic film, an amorphous carbon film, or a titanium nitride film. Themulti-layer film 12 and the single-layer film 13 are etched concurrentlyvia the mask film 11.

FIG. 2 (c) illustrates an exemplary relationship between the etchingrate of a silicon dioxide film (SiO₂) and the etching rate of a siliconnitride film (SiN) observed in an experiment performed by setting thetemperature of the lower electrode between 25° C. and −60° C. Theprocess conditions used in the experiment are described below. Here, thetemperature of the lower electrode is synonymous with the settemperature of the chiller unit 71. For example, the temperature of thelower electrode can be set at −60° C. by setting the temperature of thechiller unit 71 at −60° C.

Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)

First high-frequency power HF: 2500 W (fixed), continuous wave

Second high-frequency power LF: intermittent (repeatedly turned on andoff), 12000 W, pulse wave, duty ratio 40%

As illustrated by FIG. 2 (c), when the temperature of the lowerelectrode is set between 25° C. and −60° C., the etching rate of thesilicon nitride film (SiN) is greater than the etching rate of thesilicon dioxide film (SiO₂). The etching rate of the silicon nitridefilm becomes close to the etching rate of the silicon dioxide film whenthe temperature of the lower electrode is set at a very low temperaturenear −60° C.

The etching rate of the silicon dioxide film can be further increased byperforming intermittent etching where the second high-frequency power LFis repeatedly turned on and off. As illustrated by FIG. 2 (a), byperforming the intermittent etching, the etching rate of thesingle-layer film 13 of silicon dioxide can be made greater than orequal to the etching rate of a silicon nitride film 15.

In an etching method of the present embodiment, the process conditionsfor the intermittent etching are optimized in performing plasma etchingon the multi-layer film 12 and the single-layer film 13. Thus, accordingto the present embodiment, as illustrated by FIG. 2 (b), when themulti-layer film 12 and the single-layer film 13 are processedconcurrently, the etching rates of these films are controlled by usingintermittent etching to reduce the processing time and improve theproductivity.

First Embodiment

<Etching Process>

An exemplary etching process according to a first embodiment isdescribed with reference to a flowchart of FIG. 3. The etching processof FIG. 3 is controlled by the controller 50 in FIG. 1.

When the etching process of FIG. 3 is started, the controller 50 setsthe temperature of a wafer surface at a very low temperature of −35° C.or lower (step S10). For example, the temperature of the wafer surfacecan be set at −35° C. or lower by setting the temperature of the chillerunit 71 at −60° C. or −70° C.

Next, the controller 50 supplies a hydrogen-containing gas and afluorine-containing gas into the process chamber 10 (step S12). Forexample, a hydrogen (H₂) gas and a carbon tetrafluoride (CF₄) gas, or agas including these gases is supplied into the process chamber 10.

Next, the controller 50 causes the first high-frequency power supply 31to output and apply the first high-frequency power HF to the mount table17. Also, the controller 50 causes the second high-frequency powersupply 32 to output and apply the second high-frequency power LF to themount table 17 (i.e., to turn on the second high-frequency power LF). Asa result, the multi-layer film 12 of silicon dioxide and silicon nitrideand the single-layer film 13 of silicon dioxide are etched (step S14:first process). In the first process, the first high-frequency power HFand the second high-frequency power LF are continuous waves. The timeperiod (duration) for which the first process is performed is shorterthan the time period (duration) for which a second process is performed.For example, the duration of the first process is less than or equal toone third (⅓) of the duration of the second process.

After the first process, the controller 50 performs etching on themulti-layer film 12 and the single-layer film 13 with the output of thesecond high-frequency power supply 32 stopped (i.e., with the secondhigh-frequency power LF turned off) (step S16: second process). Next,the controller 50 determines whether a repetition count, which indicatesthe number of times the turning on and off of the second high-frequencypower LF is repeated, has reached a predetermined number of times (stepS18). The predetermined number of times is greater than or equal to two.When it is determined that the repetition count of the secondhigh-frequency power LF has not reached the predetermined number oftimes, the controller 50 causes the second high-frequency power supply32 to output the second high-frequency power LF again (step S20). Theduration of step S20 is shorter than the duration of the second process.Then, the controller 50 returns to step S16, and repeats steps S16through S20 until it is determined at step S18 that the repetition counthas reached the predetermined number of times. When it is determined atstep S18 that the repetition count of the second high-frequency power LFhas reached the predetermined number of times, the controller 50 endsthe etching process.

<Results of Etching Process>

Next, exemplary results of the above described etching process of thefirst embodiment are described with reference to FIGS. 4A and 4B. Theprocess conditions used to obtain the results of FIGS. 4A and 4B weresubstantially the same as those described above except that thetemperature of the lower electrode was set at −70° C.

In FIG. 4A, the horizontal axis indicates time and the vertical axisindicates the temperature of the wafer W. The temperature of the wafer Wwas measured based on reflected light of an infrared laser beam aimed atthe wafer W while the lower electrode was cooled to a temperature of−70° C. However, any other known method may also be used to measure thetemperature of the wafer W.

A line F indicates a case where the first high-frequency power HF of2500 W was output as a continuous wave from the first high-frequencypower 31 and the second high-frequency power LF of 12000 W was output asa continuous wave from the second high-frequency power supply 32.Because the increase in the wafer temperature varies depending on theamount of heat input from plasma, it is possible to control the wafertemperature by turning on and off the second high-frequency power LF. Asa result of continuously outputting the second high-frequency power LF,as indicated by a record No. 1 in FIG. 4B, the temperature of the waferW indicated by the line F increased to a temperature higher than −35° C.after 30 s from plasma ignition, and increased to −33° C. after 120 sfrom the plasma ignition. In this case, the difference (temperatureincrease) in the temperature of the wafer W after 120 s from the plasmaignition is 32° C.

A line E indicates a case where the first high-frequency power HF wasset at 2500 W, the second high-frequency power LF was set at 12000 W, anON time for which the second high-frequency power LF was turned on wasset at 5 s, an OFF time for which the second high-frequency power LF wasturned off was set at 15 s, and the ON time and the OFF time wererepeated 24 times. While the second high-frequency power LF is turnedoff, the generation of plasma is suppressed, the heat input from theplasma is reduced, and the increase in the wafer temperature issuppressed. As a result, as indicated by a record No. 2 in FIG. 4B, thetemperature of the wafer W indicated by the line E was −40.7° C. after120 s from the plasma ignition, and the wafer W was maintained at a verylow temperature of less than −35° C. In this case, the difference(temperature increase) in the temperature of the wafer W after 120 sfrom the plasma ignition was 24.5° C. Compared with the case (line F)where the second high-frequency power LF was output as a continuouswave, the temperature increase of the wafer W was suppressed. In thecase of the line E, however, the temperature of the wafer W slightlyincreased as illustrated in FIG. 4A. This indicates that the heat inputfrom the plasma to the wafer W was not completely eliminated.

During an etching process, the chiller unit 71 circulated a refrigerantkept at −60° C. or −70° C. through the mount table 17. Accordingly,during an etching process, heat was continuously removed from thesurface of the wafer W via the refrigerant circulating through the mounttable 17. Because the temperature of the wafer W slightly increased inthe case of the line E in spite of the heat removal by the chiller unit71, it is assumed that the OFF time of the second high-frequency powerLF is rather short.

For this reason, in the case of a line D in FIG. 4A, the OFF time of thesecond high-frequency power LF was increased from 15 s to 30 s. In thecase of the line D, the first high-frequency power HF was set at 2500 W,the second high-frequency power LF was set at 12000 W, and an ON time of5 s and an OFF time of 30 s were repeated 24 times to measure thetemperature of the wafer W during the etching process. While the secondhigh-frequency power LF was turned off, the generation of plasma wassuppressed, the heat input from the plasma was reduced, and the increasein the wafer temperature was further suppressed. As indicated by arecord No. 3 in FIG. 4B, the temperature of the wafer W indicated by theline D was −43.5° C. after 120 s from the plasma ignition, and the waferW was maintained at a very low temperature of less than −35° C. In thiscase, the difference (temperature increase) in the temperature of thewafer W after 120 s from the plasma ignition was 21.1° C. Thus, thetemperature increase was further suppressed. Thus, in the case of theline D in FIG. 4A, there was no increase in the temperature of the waferW during the etching process. This indicates that the heat input fromthe plasma to the wafer W was completely eliminated.

Based on the above results, in the etching method of the presentembodiment, intermittent etching is performed by repeatedly turning onand off the second high-frequency power LF for the ON time of 5 s andthe OFF time of 30 s. The etching method of the present embodiment makesit possible to maintain the wafer W at a very low temperature of −40° C.or lower, and makes it possible to decrease the peak temperature of thewafer W by about 11° C. compared with an etching method where the secondhigh-frequency power LF is not intermittently applied (i.e.,continuously applied). Thus, the etching method of the presentembodiment can decrease the peak temperature of the wafer W to atemperature that is lower than the temperature achievable by decreasingthe temperature of the refrigerant of the chiller unit 71 by 10° C., andcan maintain the wafer W at a low temperature during an etching process.Thus, compared with the case of the line F where the secondhigh-frequency power LF is continuously applied, the amount of heatinput to the wafer W during an etching process is greatly reduced.

As described above, unlike an etching method where the secondhigh-frequency power LF is continuously applied, the etching method ofthe present embodiment makes it possible to decrease the peaktemperature of the wafer W and maintain the wafer W at a very lowtemperature of −35° C. or lower. Accordingly, the etching method of thepresent embodiment makes it possible to etch the wafer W at a very lowtemperature of −35° C. or lower, and equalize the etching rates of themulti-layer film and the single-layer film. This in turn makes itpossible to increase the etching rates and improve the productivity.

FIGS. 5A through 5C illustrate the results of etching processesperformed under the following process conditions.

[Process Conditions]

FIG. 5A: Comparative Example

-   -   Lower electrode temperature: −60° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)    -   First high-frequency power HF: 2500 W, continuous wave    -   Second high-frequency power LF: 4000 W, continuous wave

FIG. 5B: Example of Embodiment

-   -   Lower electrode temperature: −60° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)    -   First high-frequency power HF: 2500 W, continuous wave    -   Second high-frequency power LF: 4000 W, ON 5 s/OFF 15 s    -   Repetition count: 36

FIG. 5C: Example of Embodiment

-   -   Lower electrode temperature: −60° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)    -   First high-frequency power HF: 2500 W, continuous wave    -   Second high-frequency power LF: 4000 W, ON 5 s/OFF 30 s    -   Repetition count: 36

FIG. 5A corresponds to the case of the line F in FIG. 4A where thesecond high-frequency power LF was a continuous wave. FIG. 5Bcorresponds to the case of the line E in FIG. 4A where the secondhigh-frequency power LF was a pulse wave. FIG. 5C corresponds to thecase of the line D in FIG. 4A where the second high-frequency power LFwas a pulse wave. Each of FIGS. 5A through 5C illustrates cross sectionsof the multi-layer film 12 and the single-layer film 13 etched accordingto the corresponding process conditions, the depth of etching, and theetching rate (ER).

In the comparative example of FIG. 5A, the etching rate of themulti-layer film 12 was about two times greater than the etching rate ofthe single layer film 13. FIGS. 5B and 5C illustrate the results ofetching processes performed according to the etching method of thepresent embodiment where the second high-frequency power LF wasrepeatedly turned on and off to intermittently apply the secondhigh-frequency power LF. In each of FIGS. 5B and 5C, the etching rate ofthe single layer film 13 was substantially the same as the etching rateof the multi-layer film 12. The above results indicate that the wafer Wcan be maintained at a very low temperature of −35° C. or lower bysuppressing the generation of plasma and reducing the heat input fromthe plasma during the OFF time of the second high-frequency power LF.Thus, the etching method of the present embodiment makes it possible tosubstantially equalize the etching rates of the multi-layer film 12 andthe single-layer film 13, to increase the etching rates of themulti-layer film 12 and the single-layer film 13, and to improve theproductivity.

In the process conditions, the OFF time of the second high-frequencypower LF was longer than the ON time of the second high-frequency powerLF. This makes it possible to reduce heat input from plasma and maintainthe wafer W at a very low temperature of −35° C. or lower.

In the first embodiment, only the second high-frequency power LF wasturned on and off. However, both of the first high-frequency power HFand the second high-frequency power LF may be intermittently applied. Inthis case, the first high-frequency power HF and the secondhigh-frequency power LF may be turned on and off in synchronization witheach other.

Second Embodiment

<Etching Process>

An exemplary etching process according to a second embodiment isdescribed with reference to FIG. 6. The etching process of FIG. 6 iscontrolled by the controller 50 in FIG. 1.

When the etching process of FIG. 6 is started, the controller 50 setsthe temperature of a wafer surface at a very low temperature of −35° C.or lower (step S10). Next, the controller 50 supplies ahydrogen-containing gas and a fluorine-containing gas into the processchamber 10 (step S12). For example, a hydrogen (H₂) gas and a carbontetrafluoride (CF₄) gas, or a gas including these gases is supplied intothe process chamber 10.

Next, the controller 50 controls the duty ratio of at least one of thefirst high-frequency power HF and the second high-frequency power LF,causes the first high-frequency power supply 31 to output and apply thefirst high-frequency power HF to the mount table 17, and causes thesecond high-frequency power supply 32 to output and apply the secondhigh-frequency power LF to the mount table 17. In the example of FIG. 6,the controller 50 controls the duty ratio of the second high-frequencypower LF at 50% or lower, repeats ON and OFF of the secondhigh-frequency power LF at high speed, and outputs the firsthigh-frequency power HF as a continuous wave to etch the multi-layerfilm 12 and the single-layer film 13 (step S30). After step S30, thecontroller 50 ends the etching process.

In the etching process of the second embodiment, at least one of thefirst high-frequency power HF and the second high-frequency power LF isoutput as a pulse wave at step S30. In the example of FIG. 6, the secondhigh-frequency power LF is output as a pulse wave, Ton indicates the ONtime of the second high-frequency power LF, and Toff indicates the OFFtime of the second high-frequency power LF. In this case, the frequencyof the pulse wave of the second high-frequency power LF is representedby “1/(Ton+Toff)”. Also, the duty ratio is represented by“Ton/(Ton+Toff)” indicating the percentage of the ON time Ton in thetotal of the ON time Ton and the OFF time Toff.

Preferably, however, the output of the first high-frequency power supply31 is also stopped in synchronization with the stop of the output of thesecond high-frequency power supply 32. In this case, both of the firsthigh-frequency power HF and the second high-frequency power LF areoutput as pulse waves, and the first high-frequency power HF and thesecond high-frequency power LF are set at the same duty ratio.Accordingly, the ON time of the first high-frequency power HF and the ONtime of the second high-frequency power LF become the same (Ton), andthe OFF time of the first high-frequency power HF and the OFF time ofthe second high-frequency power LF become the same (Toff). This methodmakes it possible to synchronize the output of the second high-frequencypower supply 32 with the output of the first high-frequency power supply31 at high speed, and makes it possible to synchronize the stop of theoutput of the second high-frequency power supply 32 with the stop of theoutput of the first high-frequency power supply 31 at high speed.

Thus, in the etching method of the second embodiment, both of the firsthigh-frequency power HF and the second high-frequency power LF arepreferably output as pulse waves. Also, the duty ratio of at least oneof the first high-frequency power HF and the second high-frequency powerLF is preferably less than or equal to 50% to suppress the heat inputfrom plasma and maintain the wafer W at a very low temperature of −35°C. or lower.

<Results of Etching Process>

Next, exemplary results of etching processes performed according to theetching method of the second embodiment are described with reference toFIGS. 7A through 7C. In the etching processes of FIGS. 7A through 7C,the temperature of the lower electrode was set at −70° C. FIGS. 7Athrough 7C illustrate the results of etching processes performed underthe following process conditions according to the etching method of thesecond embodiment.

[Process Conditions]

FIG. 7A: Example of Embodiment

-   -   Lower electrode temperature: −70° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)    -   First high-frequency power HF: 2500 W, pulse wave, duty ratio        40%    -   (Effective value of first high-frequency power HF: 1000 W)    -   Second high-frequency power LF: 12000 W, pulse wave, duty ratio        40%    -   (Effective value of second high-frequency power LF: 4800 W)

FIG. 7B: Example of Embodiment

-   -   Lower electrode temperature: −70° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)    -   First high-frequency power HF: 2500 W, pulse wave, duty ratio        30%    -   (Effective value of first high-frequency power HF: 750 W)    -   Second high-frequency power LF: 12000 W, pulse wave, duty ratio        30%    -   (Effective value of second high-frequency power LF: 3600 W)

FIG. 7C: Example of Embodiment

-   -   Lower electrode temperature: −70° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)    -   First high-frequency power HF: 2500 W, pulse wave, duty ratio        20%    -   (Effective value of first high-frequency power HF: 500 W)    -   Second high-frequency power LF: 12000 W, pulse wave, duty ratio        20%    -   (Effective value of second high-frequency power LF: 2400 W)

As illustrated by FIGS. 7A through 7C, in the etching method of thesecond embodiment, the etching rates can be controlled by controllingthe duty ratios of the first high-frequency power HF and the secondhigh-frequency power LF. As the results indicate, when the duty ratiowas set at 30% as in FIG. 7B, the etching rates of the multi-layer film12 and the single-layer film 13 was closest to each other. Thus, a dutyratio of 30% is suitable to concurrently processing the multi-layer film12 and the single-layer film 13. When the duty ratio was set at 40% asin FIG. 7A, the etching rate of the multi-layer film 12 was greater thanthe etching rate of the single-layer film 13. On the other hand, whenthe duty ratio was set at 20% as in FIG. 7C, the etching rate of thesingle-layer film 13 was greater than the etching rate of themulti-layer film 12.

The etching method of the second embodiment makes it possible to reducethe heat input from plasma during the OFF time by switching the ON timeand the OFF time of each of the first high-frequency power HF and thesecond high-frequency power LF rapidly. This makes it possible tosuppress the temperature increase of the wafer W and maintain the waferW at a very low temperature of −35° C. or lower. Particularly, theetching method of the second embodiment makes it possible tosubstantially equalize the etching rates of the multi-layer film 12 andthe single-layer film 13 by controlling the duty ratio. Also, theetching method of the second embodiment makes it possible to increasethe etching rates of the multi-layer film 12 and the single-layer film13 and increase the productivity.

The duty ratios of the first high-frequency power HF and the secondhigh-frequency power LF are preferably less than or equal to 50%.Setting the duty ratios at 50% or lower makes it possible to performintermittent etching where the ON time (Ton) is shorter than the OFFtime (Toff), to reliably maintain the wafer W at a very low temperatureof −35° C. or lower, to increase the etching rates of the multi-layerfilm 12 and the single-layer film 13, and to substantially equalize theetching rates of the multi-layer film 12 and the single-layer film 13.

Also, in the etching method of the second embodiment, the duty ratio ofone or both of the first high-frequency power HF and the secondhigh-frequency power LF may be controlled. In either case, the dutyratio of at least one of the first high-frequency power HF and thesecond high-frequency power LF is preferably set at a value less than orequal to 50%. This makes it possible to maintain the wafer W at a verylow temperature of −35° C. or lower, to substantially equalize theetching rates of the multi-layer film 12 and the single-layer film 13,and to increase the etching rates of the multi-layer film 12 and thesingle-layer film 13.

In the above embodiments, a hydrogen gas is used as an example of thehydrogen-containing gas, and a carbon tetrafluoride gas is used as anexample of the fluorine-containing gas. However, the hydrogen-containinggas is not limited to a hydrogen (H₂) gas, but may be any gas thatincludes at least one of a methane (CH₄) gas, a fluoromethane (CH₃F)gas, a difluoromethane (CH₂F₂) gas, and a trifluoromethane (CHF₃) gas.Also, the fluorine-containing gas is not limited to a carbontetrafluoride (CF₄) gas, but may be any one of a C₄F₆(hexafluoro-1,3-butadiene) gas, a C₄F₈ (perfluorocyclobutane) gas, aC₃F₈ (octafluoropropane) gas, a nitrogen trifluoride (NF₃) gas, and aSF₆ (sulfur hexafluoride) gas.

Third Embodiment

According to the etching method of the first embodiment, when the firsthigh-frequency power HF and the second high-frequency power LF areintermittently applied, the first high-frequency power HF and the secondhigh-frequency power LF can be turned on and off in synchronization witheach other. Also, according to the etching method of the secondembodiment, when ON and OFF of the first high-frequency power HF and thesecond high-frequency power LF are switched at high speed as illustratedin FIG. 8A “sync-pulse”, the duty ratios of the pulse waves of the firsthigh-frequency power HF and the second high-frequency power LF arecontrolled.

On the other hand, in an etching method according to a third embodiment,instead of completely stopping the output of the first high-frequencypower supply 31 in synchronization with the stop of the output of thesecond high-frequency power supply 32, the output of the firsthigh-frequency power supply 31 is reduced as illustrated by FIG. 8B“advanced-pulse”. In the example of FIG. 8B, the output value of thefirst high-frequency power HF is reduced to 100 W in the second process.However, the reduced output value of the first high-frequency power HFis not limited to 100 W, but may be any value smaller than the outputvalue in the first process.

Thus, in the etching method of the third embodiment, the output of thefirst high-frequency power supply 31 is reduced in synchronization withthe stop of the output of the second high-frequency power supply 32.With this method where the output of the first high-frequency powersupply 31 is not completely stopped, plasma is ignited even during thesecond process in FIG. 8B. For this reason, compared with the secondprocess in FIG. 8A, more anisotropic deposits of ions adhere to the sidesurface of a hole during the second process in FIG. 8B. Accordingly,compared with the etching methods of the first and second embodiments,the etching method of the third embodiment makes it possible to improvethe shape controllability in etching. Also in the third embodiment, thefirst process and the second process are repeated multiple times, andthe first process is shorter in time than the second process.

Next, exemplary results of an etching process performed according to theetching method of the third embodiment are described. FIGS. 9A and 9Billustrate the results of etching processes performed under thefollowing process conditions.

[Process Conditions]

-   -   Lower electrode temperature: −70° C.    -   Gas: hydrogen (H₂)/carbon tetrafluoride (CF₄)/trifluoromethane        (CHF₃)/nitrogen trifluoride (NF₃)/perfluorocyclobutane (C₄F₈)    -   First high-frequency power HF: 2500 W, pulse wave, duty ratio        20%    -   (Effective value of first high-frequency power HF: 500 W)    -   Second high-frequency power LF: 12000 W, pulse wave, duty ratio        20%    -   (Effective value of second high-frequency power LF: 2400 W)

FIG. 9A illustrates holes etched according to the etching method(sync-pulse) of the second embodiment, and is the same as FIG. 7C. FIG.9B illustrates holes etched according to the etching method(advanced-pulse) of the third embodiment.

In the etching method of the third embodiment, the duty ratios of thefirst high-frequency power HF and the second high-frequency power LFwere controlled, and the output of the first high-frequency power supply31 was controlled at high speed in synchronization with the stop of theoutput of the second high-frequency power supply 32 but was notcompletely stopped. As the results indicate, the etching method of thethird embodiment can improve the shape controllability in etching. Also,the results indicate that the etching method of the third embodiment cancontrol the etching rates (ER) and the etching depths similarly to theetching method of the second embodiment.

As described above, with the etching method of the third embodimentwhere the output of the first high-frequency power supply 31 is reducedbut not completely stopped in synchronization with the stop of theoutput of the second high-frequency power supply 32, it is possible toimprove the shape controllability in etching.

In the etching process of FIG. 9B, a mixed gas of hydrogen (H₂), carbontetrafluoride (CF₄), trifluoromethane (CHF₃), nitrogen trifluoride(NF₃), and perfluorocyclobutane (C₄F₈) was used. However, various typesof a hydrogen-containing gas and a fluorine-containing gas, or a mixedgas including those gases may be used in the etching method of the thirdembodiment.

Also in the third embodiment, the duration of the first process ispreferably less than or equal to one third (⅓) of the duration of thesecond process. Also, in the etching method of the third embodiment,etching may be performed either by intermittent etching where the firsthigh-frequency power supply 31 and the second high-frequency powersupply 32 are turned on and off at intervals of several seconds toseveral tens of seconds as in the first embodiment or by controlling theduty ratios as in the second embodiment.

For example, the intermittent etching method of the first embodiment maybe modified such that in the second process, the output of the firsthigh-frequency power supply 31 is reduced but not completely stopped insynchronization with the stop of the output of the second high-frequencypower supply 32 to improve the shape controllability in etching. Thismethod of reducing but not completely stopping the output of the firsthigh-frequency power supply 31 in synchronization with the stop of theoutput of the second high-frequency power supply 32 may be applied to acase where only the output of the second high-frequency power supply 32is stopped.

Also, when the second embodiment is applied to the third embodiment, theduty ratios are preferably 50% or lower also in the third embodiment.Also, in this case, the duty ratios of the first high-frequency power HFand the second high-frequency power LF are preferably the same.

Also, in the second process of the third embodiment, a first controlprocess of completely stopping both of the output of the firsthigh-frequency power supply 31 and the output of the secondhigh-frequency power supply 32 may be used in combination with a secondcontrol process of reducing but not completely stopping the output ofthe first high-frequency power supply 31 in synchronization with thestop of the output of the second high-frequency power supply 32.

Further, a direct-current (DC) voltage may be applied to the upperelectrode. In this case, the direct-current voltage applied in thesecond process may be higher than the direct-current voltage applied inthe first process.

Etching methods according to the embodiments are described above.However, the present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the present invention. Also, theembodiments may be combined as long as they do not conflict with eachother.

The etching apparatus of the above embodiments may be applied not onlyto a capacitively-coupled plasma (CCP) apparatus but also to other typesof plasma processing apparatuses. Examples of other types of plasmaprocessing apparatuses may include an inductively-coupled plasma (ICP)apparatus, a plasma processing apparatus using a radial line slotantenna, a helicon wave plasma (HWP) apparatus, and an electroncyclotron resonance (ECR) plasma apparatus.

Although the semiconductor wafer W is used as an example of an object tobe etched in the above embodiments, the object to be etched is notlimited to the wafer W. For example, the etching apparatus and theetching methods of the above embodiments may also be used to etch boardsused for a liquid crystal display (LCD) and a flat panel display (FPD),a photomask, a CD substrate, and a printed-circuit board.

An aspect of this disclosure makes it possible to improve thecontrollability of the temperature of a substrate and the etchinguniformity when concurrently etching different types of films.

What is claimed is:
 1. An etching method performed by an etchingapparatus, the etching method comprising: placing, on a mount table ofthe etching apparatus, a wafer that includes a multi-layer filmincluding a first silicon-containing film and a secondsilicon-containing film different from the first silicon-containing filmand a single-layer film including the first silicon-containing film;setting a temperature of the wafer at −35° C. or lower; supplying, by afirst radio-frequency power supply of the etching apparatus, a firstradio-frequency power with a first frequency to generate plasma from ahydrogen-containing gas and a fluorine-containing gas; performing afirst process of applying a second radio-frequency power with a secondfrequency lower than the first frequency to the mount table by a secondradio-frequency power supply of the etching apparatus; and performing asecond process of stopping the application of the second radio-frequencypower, wherein the first process and the second process are repeatedmultiple times; and the first process is shorter in time than the secondprocess.
 2. The etching method as claimed in claim 1, wherein in thesecond process, the supply of the first radio-frequency power is alsostopped in synchronization with the stopping of the application of thesecond radio-frequency power.
 3. The etching method as claimed in claim1, wherein a duration of the first process is less than or equal to onethird of a duration of the second process.
 4. The etching method asclaimed in claim 1, wherein the hydrogen-containing gas is a hydrogen(H₂) gas and the fluorine-containing gas is a carbon tetrafluoride (CF₄)gas.
 5. The etching method as claimed in claim 1, wherein themulti-layer film and the single-layer film are etched by the generatedplasma; and in the second process, the supply of the firstradio-frequency power is reduced in synchronization with the stopping ofthe application of the second radio-frequency power.
 6. An etchingmethod performed by an etching apparatus, the etching method comprising:placing, on a mount table of the etching apparatus, a wafer thatincludes a multi-layer film including a first silicon-containing filmand a second silicon-containing film different from the firstsilicon-containing film and a single-layer film including the firstsilicon-containing film; setting a temperature of the wafer at −35° C.or lower; supplying, by a first radio-frequency power supply of theetching apparatus, a first radio-frequency power with a first frequencyto generate plasma from a hydrogen-containing gas and afluorine-containing gas; applying a second radio-frequency power with asecond frequency lower than the first frequency to the mount table by asecond radio-frequency power supply of the etching apparatus, at leastone of the first radio-frequency power and the second radio-frequencypower being a pulse wave; and controlling a duty ratio of the pulsewave.
 7. The etching method as claimed in claim 6, wherein the dutyratio is less than or equal to 50%.
 8. The etching method as claimed inclaim 7, wherein both of the first radio-frequency power and the secondradio-frequency power are pulse waves; and the duty ratio of the firstradio-frequency power is the same as the duty ratio of the secondradio-frequency power.
 9. The etching method as claimed in claim 6,wherein the hydrogen-containing gas is a hydrogen (H₂) gas and thefluorine-containing gas is a carbon tetrafluoride (CF₄) gas.
 10. Theetching method as claimed in claim 6, wherein the multi-layer film andthe single-layer film are etched by the generated plasma; and the supplyof the first radio-frequency power is reduced in synchronization withstopping the application of the second radio-frequency power.
 11. Anetching method performed by an etching apparatus, the etching methodcomprising: placing, on a mount table of the etching apparatus, a waferthat includes a multi-layer film including a first film and a secondfilm different from the first film and a single-layer film including thefirst film; outputting, by a first radio-frequency power supply of theetching apparatus, a first radio-frequency power with a first frequencyto generate plasma from a process gas; applying a second radio-frequencypower with a second frequency lower than the first frequency to themount table by a second radio-frequency power supply of the etchingapparatus; and stopping the application of the second radio-frequencypower, wherein the application of the second radio-frequency power tothe mount table and the stopping of the application of the secondradio-frequency power are repeated to concurrently etch the multi-layerfilm and the single-layer film.
 12. The etching method as claimed inclaim 11, wherein a duration of the application of the secondradio-frequency power to the mount table is shorter than a duration ofthe stopping of the application of the second radio-frequency power.